[flang][OpenMP] fujitsu 1037/1037_0048.f90 unexpected 'fir.is_present' op operand #0 must be any reference or box like

[sscalpone]

% flang -fopenmp 1037/1037_0048.f90
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
error: loc(".../1037/1037_0048.f90":21:7): 'fir.is_present' op operand #0 must be any reference or box like, but got 'i32'
error: verification of lowering to FIR failed

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: Steve Scalpone (sscalpone)

% flang -fopenmp 1037/1037_0048.f90
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
error: loc(".../1037/1037_0048.f90":21:7): 'fir.is_present' op operand #<!-- -->0 must be any reference or box like, but got 'i32'
error: verification of lowering to FIR failed

[tblah]

@kparzysz the line generating the error is an omp atomic. Would you like to look into this or should i do it?

[kparzysz]

This may be something new. It passed when I ran my tests.

[kparzysz]

Reduced testcase

subroutine ss2(a, x)
  integer :: a
  integer, optional :: x
  !$omp atomic update
  a = max(x, a, x)
end

[kparzysz]

Here's what happens:
The "min" and "max" intrinsics take a variable number of arguments, 2 or more. If the trailing argument(s), beyond the 2nd one, are optional, the lowering code will treat them specially by generating the "is_present" call. If they are absent the call can be treated as if they weren't listed as arguments to begin with.

What's worse is that "min" and "max" are just expanded into a series of compare/select operations, which makes is unsuitable for an atomic operation with more than 2 arguments.

I don't know how this test passed before. 😕

[kkwli]

I don't know the original test but

!$omp atomic update
  a = max(x, a, x)

is invalid.

"None of v, x, d, r, expr, and expr-list (as applicable) may access the same storage location as any other symbol in the list."

[kparzysz]

True, here's a more compliant testcase:

subroutine ss2(a, x, y)
  integer :: a
  integer, optional :: x, y
  !$omp atomic update
  a = max(x, a, y)
end

[kparzysz]

I'm going to have the compiler rewrite it as

tmp = max(x, x, y)
!$omp atomic update
a = max(tmp, a)

[eugeneepshteyn]

@kparzysz , since you mention rewriting things, please also take a look at #144944